Table of contents

This review is devoted to a new method in experimental physics—electron cooling, which opens the possibility of storing intense and highly monochromatic beams of heavy particles and carrying out a wide range of experiments with high luminosity and resolution. The method is based on the cooling of beams by an accompanying electron flux as the result of Coulomb collisions of the particles. In the first part of the review the theoretical basis of the method is briefly considered. The apparatus NAP-M is described with its electron cooling, and the results of successful experiments on cooling a proton beam are presented. In the second part the new possibilities opened by the use of electron cooling are discussed: storage of intense beams of antiprotons and achievement of proton-antiproton colliding beams, performance of experiments at the ultimate in low energies (with participation of antiparticles), storage of polarized antiprotons and other particles, production of antiatoms, storage of antideuterons, and experiments with ion beams.

A review is given of the current status of research on photoelectromagnetic effects. A detailed analysis is made of the results of the more recent experimental studies of the anisotropy of the even and odd photoelectromagnetic effects, the effect across p–n junctions, the effect at low temperatures (when the electron system is heated by the incident radiation and the electron temperature is higher than the lattice temperature), and the radiation electromagnetic effect (when a sample in a magnetic field is not illuminated but irradiated with a flux of ionizing particles). The experimental data are compared with the theory. Directions of future studies of the photoelectromagnetic effect are suggested.

Some typical resonance nonlinear-optics phenomena taking place when light interacts with atoms are considered. The multitude of such phenomena reduces to scattering of the perturbing light, perturbation of the atomic spectrum, excitation of an atom and its ionization. In all these cases the investigations are carried out using the simplest model—an isolated atom in a monochromatic external field. Such a model enables one to give an exact description of many elementary processes. On the other hand it is sufficiently realistic. A detailed investigation is carried out of resonance fluorescence, spontaneous Raman scattering, multiphoton excitation of atoms, resonance shifts and splitting of atomic levels and resonance lonication of atoms. The nature of these processes is investigated as a function of the intensity of the external field, its frequency, a specific atomic spectrum, the nature of polarization of the perturbing field, and the degree of its nonlinearity. The role played by the field of the electromagnetic vacuum is analyzed. Theoretical predictions are compared with the results of many experiments describing resonance processes of the interaction of an intense light field with atoms.

CONTENTS 1. Protons, Neutrons, Hadrons and Their Structure 328 2. A Simple Picture of Diffraction Scattering 329 3. Experiments on Total Cross Sections 332 3.1 Good geometry transmission experiments 332 3.2 Colliding beam experiments 332 3.3 Results on total cross sections 335 4. Experiments on Elastic Scattering 335 4.1 Scattering in the Coulomb region 335 4.2 Scattering at intermediate momentum transfers 338 4.3 Scattering at large momentum transfers 339 5. What Have We Learned From Hadron-Proton Scattering? 340 5.1 Energy dependence of total cross-sections 340 5.2 Elastic cross-sections and hadron-proton absorptiveness 341 5.3 Diffraction scattering and hadron structure 342 References 343

The fulfillment in quantum electrodynamics of the principle of relativistic causality—the signal velocity does not exceed the velocity of light—is discussed. In Sec. 1 it is argued that this principle is not guaranteed automatically merely by the local commutativity of the theory. Section 2 is a critical review of the signal transmission problems which have been formulated and solved in the literature. In Sec. 3, this problem is considered in the framework of a simple but fairly realistic model of quantum electrodynamics. The signal source is an external current localized in some region S. The arrival of a signal in a region D at a distance R is established by a change in the coordinate, momentum, or energy of a charged particle. It is shown that proof of relativistic causality of the theory requires one to take into account appropriately quantum-mechanical and, in particular, quantum-electrodynamical features of the problem. In the final fourth section, a general formulation and exact solution of the signal transmission problem are given. The treatment is of sufficient generality for one to be able to assert that in the framework of quantum electrodynamics none of the possible methods of signal transmission violate relativistic causality.